Attitude control in many spacecraft is implemented using one or more control moment gyros (CMGs). A CMG is a torque-generating mechanism that may include a rotating flywheel, or rotor, that is rotationally mounted in a gimbal. A spin motor may be coupled to the rotor and may be energized and controlled to rotate the rotor about a spin axis at a substantially constant rotational velocity. The gimbal may be rotationally mounted about one or more gimbal axes, which are perpendicular to the spin axis. Additionally, one or more gimbal motors may be coupled to the gimbal and, in response to gimbal rate commands, may rotate the gimbal about one or more of the gimbal axes. By rotating the frame about one or more of the gimbal axes at certain rates, torques can be generated in the spacecraft body to implement spacecraft attitude control.
It is postulated that the above-described CMGs could undergo certain unlikely events. Such unlikely events include, for example, the gimbal feedback path being opened or otherwise becoming unavailable. If such an unlikely event were to occur, the CMG could become unstable and the CMG gimbal rate could reach levels that could potentially damage the CMG. To prevent gimbal rates from reaching such levels, many CMGs include a mechanism to detect a gimbal over rate and disable the gimbal upon detecting the gimbal over rate. Unfortunately, with presently known systems and methods, there is an undesirable time delay between detecting the over rate condition and disabling the CMG.
Hence, there is a need for a system and method of preventing CMG gimbal overate that does not include an undesirably long time delay, and that does not interfere with the typical rate overshoot that the CMG encounters during normal operations. The present invention addresses at least this need.